The long term goal of this project is to understand the structural basis of substrate recognition and catalytic mechanism for a group of acyltransferases. Based on sequence homology and reaction mechanism, these acyltransferases constitute a unique gene family which serve crucial physiological roles. For instance, carnitine palmitoylransferase I and II are essential for b-oxidation of long chain fatty acids in mitochondria and are responsible for excessive rates of fatty acid oxidation in pathological states such as diabetes and ketosis. Choline acetyltransferase is responsible for the biosynthesis of the neurotransmitter acetylcholine; a deficiency in the enzymatic activity has been correlated with the loss of cognitive functions in Alzheimer's disease. The other acetyltransferase of this family, carnitine acetyltransferase, plays an important role in the maintenance of mitochondrial CoASH/acetylCoA balance, cellular energy metabolism, detoxification and cell cycle regulation. Acetylcarnitine was reported to protect neuronal cell loss in ischemia and improve cognitive functions in Alzheimer's disease patients. A deficiency or acetylcarnitine in sera of a group of AIDS patients was recently reported in a severe dose-limiting axonal peripheral neuropathy caused by several antiretroviral agents such as ddl, ddC and d4T. Therefore, molecular analysis of these acyltransferases is of significance to our understanding of the mechanisms of enzyme action as well as the mechanisms involved in pathological conditions. In this proposal, we will focus on the structure/function/regulatory relationship of these acyltransferases. Specifically, we propose to determine the structural basis of substrate recognition of these acyltransferases using a combination of biophysical and molecular genetic approaches.